Fluorosilicone elastomer compositions have been used for aircraft and automobile rubber parts in view of their high resistance to gasoline and oils. Fluorosilicone elastomer compositions have also been used as a protective material for elements of an air amount sensor for fuel injection control in automobiles, a gasoline vapor pressure sensor in a gasoline tank, and a liquid and gas pressure sensor in fuel feeding systems.
Various curable fluorosilicone compositions for such applications has been disclosed, for example, in JP-B 53-35983, JP-B 59-31542, and JP-B 60-27691 as well as JP-A 57-182353 and JP-A 59-80464.
However, fluorosilicone polymers suffer from the drawback of extremely poor defoamability. For example, in the case of a two part curable fluorosilicone composition, the composition is used by mixing the base component and the curing agent at a predetermined mixing ratio before its use, and the bubbles entrained in the mixing should be completely removed by means such as vacuum deaeration. In the meanwhile, one part curable fluorosilicone composition not requiring such mixing before its use suffered from the problem of bubbles remaining in the potting layer when used for the potting of a substrate for electric/electronic parts since removal of bubbles caused by the gap in the board had been difficult.